Chapter 17 - Chapter 17 Applications of Infrared...

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Unformatted text preview: Chapter 17 Applications of Infrared Spectrometry Infrared spectrometry is applied to the qualitative and quantitative determination of molecular species of all types. The most widely used region is the mid-infrared that extends from about 670 to 4000 cm-1 (2.5 to 14.9 m). The near-infrared region from 4000 to 14,000 cm-1 (0.75 to 2.5 m) also finds considerable use for the routine quantitative determination. The far-infrared region has been for the determination of the structures of inorganic and metal-organic species. MID-INFRARED ABSORPTION SPECTROMETRY Sample Handling No good solvents exist that are transparent throughout the region of interest. As a consequence, sample handling is frequently the most difficult and time-consuming part of an infrared spectrometric analysis. Gases: The spectrum of a low-boiling liquid or gas can be obtained by permitting the sample to expand into an evacuated cylindrical cell equipped with suitable windows. Sample Handling Solutions: A convenient way of obtaining infrared spectra is on solutions prepared to contain a known concentration of sample. This technique is somewhat limited in its applications, however, by the availability of solvents that are transparent over significant regions in the infrared. Solvents: No single solvents is transparent throughout the entire mid-infrared region. Water and alcohols are seldom employed, not only because they absorb strongly, but also because they attack alkali-metal halides, the most common materials used for cell windows. Sample Handling Cells: Sodium chloride windows are most commonly employed; even with care, however, their surfaces eventually become fogged due to absorption of moisture. Polishing with a buffing powder returns them to their original condition. Liquids: When the amount of liquid sample is small or when a suitable solvent is unavailable, it is common practice to obtain spectra on the pure (neat) liquid. A drop of the neat liquid is squeezed between two rock-salt plated to give a layer that has a thickness of 0.01 mm orplated to give a layer that has a thickness of 0....
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Chapter 17 - Chapter 17 Applications of Infrared...

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